1. Field of the Invention
This invention relates to electrophotographic apparatus and methods wherein the photoconductor material is periodically replaced. More particularly, the present invention relates to automatic replacement of photoconductor material in a web form in the environment of electrostatic copiers and printers. The invention is especially useful in that it allows automatic replacement of photoconductor panels in the imaging zone of copiers/printers in a manner that is transparent to the user, while not detracting from the machine throughput.
2. Description of the Prior Art
Contemporary xerographic copiers/printers in some cases include webs of photoconductor material that are automatically replaced in the image area of the machine by mechanisms internally to the machine. For instance, the IBM Series III Copier/Duplicator has a pair of supply spools, each containing a roll of photoconductor material which exits through drum seals onto two separate peripheral areas of the photoconductor drum. These flexible photoconductor webs each return to the inside of the drum through yet another drum seal and are attached to take-up spools. An internal gearing arrangement is attached to each take-up spool and is selectively actuable by a clutch configuration. Thus, the drum with the photoconductor normally stays in place and rotates with the drum in its imaging and image transferring operations, while the panel replacement is periodically accomplished by actuation of the clutch to engage the drive for the gears. The take-up rolls are rotated for a distance adequate to allow replacement of the panels on the drum periphery with a sensor associated with the amount of photoconductor thus dispensed causing termination of the panel replacement operations.
The quality of copies produced from the photoconductor material deteriorates for any of several different reasons. For instance, the photoconductor has a certain life associated with its usage, and it is known that the imaging area panel requires replacement at some time associated with the end of that life. The photoconductor occasionally also is damaged or scratched and requires replacement. Thus, some present copiers include arrangements for automatically feeding a new photoconductor panel to the imaging area after a predetermined copy count is reached, although they often further include the ability to allow this incrementing if the servicing personnel determine that such replacement is necessary.
In prior art copiers/printers having selectively operable mechanisms for dispensing photoconductor web, the actual photoconductor panel replacement in the image area is essentially performed by one of two processes. For instance, the copying process is interrupted and dummy machine operations performed after a predetermined copy count is reached as is taught in U.S. Pat. No. 3,588,242 filed Jan. 15, 1969 by R. A. Berlier and R. W. Rice. The disadvantage of this approach is the machine is not available to the user during the panel replacement operations. This is especially inconvenient if the interruption occurs in the middle of a copy/print job. Occasionally, operators are unaware of the function underway and remove main power from the machine believing that a malfunction has occurred.
The other approach is to periodically advance small amounts of photoconductor after a copying operation is completed so that the image area photoconductor panel is effectively exchanged in increments. This is suggested in U.S. Pat. No. 3,984,241 filed Nov. 5, 1974 by E. Schrempp and H. S. Hazelton, Jr. The disadvantage of such systems is that the complete photoconductor panel is not replaced and the quality of copying in different areas of the photoconductor differs as a function of the age of the photoconductor areas.
The present invention overcomes the disadvantages of the prior art photoconductor panel replacement systems by advantageously employing the drum rotation during its run-out phase instead of interrupting the copy job or incrementally changing the photoconductor. In this application, the "run-out" phase is considered the time between transfer of the last image from the photoconductor to a copy sheet, and the time that the machine is finally shut down at the end of the run, as when the last copy sheet is completely processed and delivered to an output such as an exit tray or the like.